New System VS Renovation of an Existing System

Very often new home owners that appreciate and value the newly acquired property's curb appeal experience doubts on whether to have a new system installed or renovate an existing system. As a professional design and planning Consultant, as well as a Certified Landscape Irrigation Auditor my advise is the following.
1- If the system is around or older than 10 years, or has also been worked on by several persons ranging from DIY past owners, to landscape maintenance contractors; It is most likely better to go ahead and INVEST on having a new system installed. The operation of an irrigation system is going to require a long term financial commitment to operate it. The operation and scheduling of the system is going to have an impact on the property's value through curb appeal. The cost of operating and constantly repairing an old system that frequently stresses plant material, as well as possibly stain, or even deteriorate the surrounding hardscape/dwelling(s) is going to cost more (over the mid term - 5+ years) than to have a new system designed, installed and properly managed.
2- If the system is around 10 years but its operation has been reliable and satisfactory, have a qualified professional like an Irrigation Auditor to review it, and give corrective Action recommendations, and also scheduling recommendations.
3- If the system is less than three years old and there are record documents that show the layout as well as what was installed and how to activate it; Talk it over w/ the person in charge of the landscape maintenance and ask for their feed back. If you are going to be the person maintaining and managing, invest the time and effort necessary to become familiar with it through a person that is familiar w/ the system.